Autoimmune diseases are associated with a loss of immunological tolerance, a failure of an organism's adaptive immune cells to distinguish between 'self' and 'non-self'. While the existence of B cell central tolerance (in the bone marrow) is now well-established, our knowledge about the cellular and molecular mechanisms of peripheral tolerance (in peripheral lymphoid organs) and their perturbation in autoimmune diseases such as 'lupus' is limited. Understanding peripheral B cell tolerance is important as perturbed regulation of these tolerance mechanisms may allow for the development of autoreactive B cells and pathogenic IgG autoantibodies that contribute to autoimmune diseases such as systemic lupus erythematosus (SLE). Here, we have used a B cell antigen receptor (BCR) knock-in mouse model (HKIR) that yields dual-reactive {Arsonate (Ars) and DNA-chromatin-self-antigen- reactive} B cells. We previously showed that dual-reactive HKIR B cells can develop into follicular B cells and differentiate into antibody forming cells (AFCs) upon immunization with Ars-conjugated foreign antigen. These dual-reactive cells also can enter germinal centers (GCs), but due to their autoreactivity are negatively regulated or prevented from expanding in GCs by a GC tolerance mechanism and do not efficiently become memory B cells. Therefore, in contrast to other autoreactive transgenic mouse models in which B cells are excluded from the peripheral lymphoid follicles including AFC and GC pathways, the HKIR model is well suited to study AFC and GC-mediated B cell tolerance pathways of nuclear-Ag-specific HKIR B cells that regulate autoantibody production. Our published and preliminary data indicate that peripheral B cell tolerance operative in the AFC and GC pathways can be altered in the presence of lupus susceptibility locus Sle1. However, the influence of Sle1 on the AFC and GC-memory tolerance appeared to be incompletely penetrant indicating the possible requirement of defects in T and/or myeloid compartments for such loss of peripheral B cell tolerance leading to production of IgG ANAs and development of lupus. Here, we propose to identify the susceptibility gene(s) within the Sle1 locus that drive B cell development into AFC and GC pathways leading to loss of peripheral B cell tolerance (Aim-1). In Aim-2, we will determine the cell type (T and/or DCs) affected by the susceptibility gene(s) within the Sle3 interval that provides B cell help and thus promotes a break in GC tolerance. In Aim-3, we will study how type I IFNs (IFN-1) may accelerate the process of a break in GC-memory tolerance and permits robust autoantibody production in lupus-prone mice.